docs: def select_functions(expr):
      """ Create the function expressions for selection """
      body = Group(expr)
      return Group(
          function("timestamp", body, caseless=True)
          | function("ts", body, caseless=True)
          | function("utctimestamp", body, caseless=True)
          | function("utcts", body, caseless=True)
          | function("now", caseless=True)
          | function("utcnow", caseless=True)
      ).setResultsName("function")